This invention relates to radar systems and more particularly to a radar receiver adapted to suppress signals from interference sources through sidelobe cancellation.
Sidelobe cancellation is a process by which interfering signals (such as produced by jammers) received through the sidelobes of an antenna are suppressed. One or more omnidirectional antennas for receiving interfering signals are located near the principal antenna which also receives the undesired interfering signal. Optimum amplitude and phase modulations are applied to this signal which is then subtracted from the principal antenna signal. By having the proper phase and amplitude modulation applied, cancellation of the undesirable signals is achieved. The modulation values are derived by correlating the principal antenna output after subtraction of the modulated omnidirectional antenna signals with the omnidirectional antenna signals. These values are applied in a feedback loop such that the cancellation process is continous and automatic. U.S. Pat. No. 3,881,177 is one such system. However, there are drawbacks to the sidelobe cancelling system disclosed in U.S. Pat. No. 3,881,177.
One principal drawback is that system does not provide any means for filtering out radar target signals and clutter either in the frequency domain or time domain. With such means provided the reduction of the canceller response to clutter return can be a significant factor in improving the performance of the system under severe clutter conditions.
The system disclosed in said patent also is unduly inefficient in that it unnecessarily requires additional amplifiers and mixers since it does not utilize the circuitry within the radar receiver itself in the processing. Furthermore, the system disclosed in said patent requires an i.f. translation.